The invention relates to a fuel tapping device for a motor vehicle heater which taps fuel from a fuel storage tank of a motor vehicle's fuel supply unit and feeds the fuel to the motor vehicle heater by a connecting pipe.
To tap fuel from the motor vehicle's fuel supply unit for an auxiliary motor vehicle heater that is able to be operated independently of the vehicle engine, there are several possibilities. Devices designed as so-called tank taps for tapping fuel can be gathered from the bibliographic reference of Webasto "Short Installation Proposal for Air Heaters" with identification number 770941, printed in the year 1991. In cases of fuel storage tanks made of plastic, of a motor vehicle's fuel supply unit, the tapping of fuel takes place by a hollow screw with a circular tube piece, which is replaced by the usually present drain plug on the underside of the fuel storage tank. Such a tapping of fuel is subject to risks with respect to safety since fuel can run out into the motor vehicle heater in the case of damage to the fuel pipe. Further, for installation, the fuel storage tank has to be completely emptied. As a result, the installation of such a fuel tap is expensive.
In the situation where the fuel storage tank of a motor vehicle's fuel supply unit is formed of metal, an additional opening can be drilled in the tanks, into which a corresponding tank tap can be inserted which serves to supply the motor vehicle heater with fuel. When the bore is drilled in the fuel storage tank, chips can drop into the tank, and these chips can cause the fuel supply to be interrupted. There is also the danger of a sparking during drilling, so that such an installation involves a certain safety risk when installation is performed after a vehicle has been put into use (i.e., retrofit installation instead of assembly line installation). Further, there is also the fact that, depending on the design of the motor vehicle, as in platform vehicles, the fuel storage tank can be difficult to access from above, so that in the extreme case, even the entire fuel storage tank has to be removed.
Further, in bibliographic reference "Installation Instructions" of Webasto with identification number 238224, published in the year 1989, a fuel tap is described on page 9 which is designed as a T-piece and is placed in the fuel feed pipe leading from the fuel storage tank to the internal combustion engine to create a branch to a metering pump for the auxiliary heater. But, in such a fuel tap, the fuel supply of the auxiliary motor vehicle heater is exposed to pressure fluctuations, which unavoidably occur in the motor vehicle's fuel supply unit. As a result, trouble disconnections of the auxiliary motor vehicle heater can occur, and further, a fuel metering pump has to be used with the auxiliary motor vehicle heater to assure as reliable and uniform as possible a fuel supply.